The present invention relates, in general, to projection screen masking systems, and more particularly to motorized bottom masking apparatus for motion picture screens, particularly wide and/or curved motion picture screens.
Since the size of the image projected onto the screen in a motion picture theater can vary depending upon the type of film being shown, the projection screen is customarily designed to accept the largest image to be shown and is then "masked", or reduced in size by a masking system, for showing smaller pictures. This masking system usually is motor-operated and comprises dark fabric mask sections which are lowered at the top of the screen and sometimes drawn toward the center of the screen from each side. Sometimes, top masking only is used, boundaries of the projection screen is used, and sometimes masking at the top and both sides, or at the top and bottom and both sides, is employed.
On small straight projection screens, bottom masking can be employed, in addition to the top masking, or the top masking and side masking, by providing cables running along the sides of the screen which lift the bottom masking to the desired elevational level. With larger screens, especially with curved screens, lifting of the bottom mask by cables running along the sides of the screen becomes virtually impossible, because the bottom masking structure sags and twists. It is not possible to provide intermediate lift cables, because this would involve running them down in front of the screen and thus would distort the image seen by the viewers. If bottom masking is simply not used, the bottom of the screen must be left bare when smaller films are shown, because the center of focus of the projector cannot easily be lowered to bring the bottom margin of the projected image down to the bottom of the screen.
An object of the present invention is the provision of a motorized bottom masking assembly for a large curved projection screen, for example, a theater screen about 42 feet wide, wherein masking is operated by motorized lift structure located entirely below the bottom masking section, eliminating the need for lift cables depending from ceiling or overhead structure above the screen and yet maintaining true horizontal alignment of the upper edge of the bottom mask without center sagging.
Another object of the present invention is the provision of a motorized bottom masking assembly for large curved projection which provides rapid raising and lowering of the bottom masking by a motorized system not involving hydraulics, and which is mounted on the floor of the theater stage below the projection screen. In a preferred embodiment, the bottom masking system involves three motorized jacks supporting a curved aluminum pipe or channel which forms the top edge of the bottom masking, the jacks being operated by variable speed DC motors which can be set to raise and lower the pipe or channel in unison at the required speed.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.